Magnetic vibratory chopper



June 29, 1965 H. REIFEL 3,192,341

MAGNETIC VIBRATORY CHOPPER .55. Filed June 18. 1963 1 l9 I 1 i v a United States Patent ,3 V a. MAGNETIC VIBRATORY CHOBPER 7 Harry Reifel, Waltham, Mass., assignor to Stevens-Arnold Inc'., South Boston, Mass, a corporation of Massachusetts I Filed June 18, 1363, Ser. No. 288,646 12 Claims. (Cl. 200-90) This invention relates to electromagnetic switches, and relates more particularly to choppers having switches of the make-befo're-break type.

Choppers are widely used for converting small D.C. signals to corresponding A.C. signals so that they can be amplified. A conventional chop-per having switches of the make-before-break type consists of a reed which in its normal mid-position,- engages a contact with each of its opposite sides. A.C. at the resonant frequency or the reed flows through an electromagnetic coil in the field of which the reed is located. During one half-wave, the reed is deflected away from one contact, and during the other half-wave, the reed is deflected away from the other contact. Usually, there is about a overlap period during which the reed touches both contacts. Such a chopper can be used effectively only at frequencies at or near the resonant frequency of its reed.

This invention provides a chopper having switches of the make-before-break type which will operateeffectively over a wide range of frequencies. In one embodiment of the invention, there are two reeds energized by a single coil, each reed having a contact which it normally touches. The reeds are magnetically polarized so that one reed moves away from its contact during one half-wave, and the other reed moves away from its contact during the opposite half-wave. The reeds are adjustably, mechanically biased towards their respective contacts so that their on times can be adjusted over a wide range.

An object of this invention is to provide a make-beforebreak type chopper which can be operated effectively over a wide range of frequencies.

Another object of this invention is to provide an electromag'ne'tic switch having on and ofl switching contacts, and the on and otI periods of which can easily be adjusted over a wide range.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a plan view looking downwardly on a chopper embodying this invention;

FIG. 2 is a side elevation of the chopper;

FIG. 3 is a section along the lines 33 of FIG. 2;

FIG. 4 is a section along the lines 4-4 of FIG. 3;

FIG. 5 is a section along the lines 55 of FIG. 3; and

FIG. 6 is a plot of the current waveform indicating operational points for a chopper embodying this invention.

A frame for the chopper consists of two aligned, parallel, metal plates 10 which are spaced apart at corresponding ends by spacers 11, 12 and 13 of electrical insulation. Metal screws 15 extend through metal straps 16 on the outer side of one of the plates 10, and extend through the plates 10 and the spacers 11, 12 and 13, and are threaded into metal strips 17 on the outer side of the other plate 10. Aligned contact pins "18 extend through the spacer 11. Contact straps 19 and 19A extend between the spacers 11 and 12, and contact straps 20 and 20A extend between the spacers 12 and 13.

3,192,341 Patented June 29, 1965 'ice The other ends of the plates 10 are spaced apart by a metal bar 21. Metal screws 22 extend through a metal strap 23 on the outer side of one of the plates 10, through the plates 10 and the bar 21, and are threaded into a metal strap 24 on the outer side of the other plate 10. The bar 21 has a central opening 26, and has a recess 27 at the outer end of the opening 26 for receiving aligned reed bases and 31 which have wedge-shaped inner ends. The bar 21 has sharp edges 28 and 29 at the outer end of the opening 26 which contact the slanted sides of the bases 30 and 31 respectively. The base 30 is adjustably attached to the bar 21 by metal screws 32 and 33 which extend through the base 30 and are threaded into the bar 21. The base 31 is adjustably attached to the bar 21 by a screw 34 which corresponds to the screw 32, and by another screw which is not shown and which corresponds to the screw 33. The bases 30 and 31 have the outer ends of reeds 35 and 36 respectively, of magnetic spring metal inset therein so as to be cantilever supported thereby. The reeds extend through the opening 26. The free end of the reed 35 has a U-shaped, contact ribbon 39 of precious metal insulatedly attached thereto as disclosed in my co-pending application, Serial No. 118,827, filed June 22, 1961, now Patent No. 3,151,228. The ribbon 39 extends between contact strips 37 and 38, and is normally biased towards so as to bein contact with the strip 38, caused by the screw 32 being threaded further into the bar 21 than the screw 33 is so that the base 30 is tilted to the right to cause the free end of the reed 35 to be tilted to the right as shown by FIG. 4. The free end of the reed 36 has a U-shaped, contact ribbon 40 of precious metal insulatedly attached thereto as disclosed in said application. The ribbon 40 extends between contact strips 41 and 42, and normally is biased towards so as to be in contact with the strip 42, caused by the screw 34 being threaded into the bar 21 further than said screw which corresponds to the screw 33 is, so that the base 31 is tilted to cause the free end of the reed 36 to be tilted to the right as is the free end of the reed 35 shown by FIG. 4. FIG. 5 shows the contact ribbons 39 and 40 normally in contact with the contact strips 38 and 42 respectively.

Extending around intermediate portions of the reeds 35 and 36 is a spool of electrical insulation having an electromagnetic coil 51 therearound. The outer end of the spool 50 rests on the inner end of the bar 21. In

contact with the inner end of the spool 50 and extending between the latter and the free ends of the reeds 35 and 36, and spaced therefrom throughout their range of vibration, are aligned permanent magnets 52 and 53 on opposite sides of the reeds. The magnets 52 and 53 have central recesses 54 and 55 respectively, for causing the magnets to act somewhat as horseshoe magnets. The north pole of one magnet is opposite the south pole of the other magnet and vice versa. This polarizes the reeds 35 and 36 oppositely magnetically so that when A.C. is applied to the coil 51, the contact ribbon on the free'end of one reed moves away from the contact strip with which it is normally in contact, during the positive half-waves, and the contact ribbon on the free end of the other reed moves away from the contact strip with which it is normally in contact, during the negative half-waves.

The contact ribbons 39 and 40 are electrically connected by flexible wires 69 and 61 respectively, to the realso,

spective contact pins 13. The contact strips 3'? and 33 are attached to the straps l9 and .29 respectively. The contact strips 41 and are attached to the straps la' A and 243A respectively. The lower ends of the straps 19 and 20 contact the strips 3'? and 38 in dampcring action, and the lower ends of the straps 19A and ZtlA contact the strips 41 and 42 in dampcring action as is disclosed in my Patent No. 2,491,907.

In the illustrated embodiment of the invention, the contact strips 37 and 41 "crform no electrical function, and are connected to no circuit components. They serve as reed stops. They could, of course, be used electrically if so desire In the illustrated embodiment of the invention, the ribbons 39 and 4d are connected together through the pins 18 by a wire 7d. The straps 20 and 26A are connected to wires '71 and 72 respectively. The st aps 1% and 19A are connected to wires 73 and '74 respectively.

In a chopper circuit, the wire 76 would be connected to a DC. signal source, the wires '71 and 72 would be connected to the ends of a center-tapped, primary winding of an input transformer of an amplifier, and the ccnter-tap of the winding would be connected to the DC. source, in a mal e-before-break circuit, as disclosed in my copending application, Serial No. 231,995, filed August 1, 1962.

With reference to FIG. 6, in operation, during each positive half-wave, the contact ribbon 39 of the reed 35 would remain in contact with the contact strip 313 until the current in the-coil 51 rises to the value A. which is sufficient to overcome the forces holding the ribbon 39 against the strip 38. The ribbon 3% would then move away from the strip 38 and remain away from the latter utnil the current falls below the value B. During each negative hal wave, the contact ribbon at of the reed 36 would remain in contact with the contact strip 42 until the current in the coil 51 rises to the value C which is sufiicient to overcome the forces holding the ribbon 46 against the contact strip 42. The ribbon it would then move away from the strip 42 and remain away from the latter until the current in the coil 51 falls below the value D. During the interval betwen the points B and C, both ribbons 39 and 4% would be in contact. with their contact strips 355 and 42 respectively, in an overlap period.

The reed bases 3d and 31 can be easily adjusted to provide more or less mechanical bias so as to require more or less respectively, electromagntic force to move their respective contact ribbons away from the contact strips with which they are normally in contact. Thus, the on times, the off times, and the overlap times can easily be adjusted.

Current at the resonant frequency of the reeds does not have to be applied to the coil 51 as in prior choppers. In the embodiment of the invention shown by the drawings, the natural resonant frequency of the reeds is 180 cps. The chopper operates uniformly at all frequencies up to 130 cps. Thus, one chopper can be used to operate over a wide range of frequencies. The range of frequencies within which the chopper will operate satisfactorily can be changed to suit operating requirements by changing the dimensions and spacings, etc, of the reeds and other components.

What is claimed is:

1. An electromagnetic switch comprising a pair of reeds of magnetic spring metal, said reeds having corresponding sides spaced apart in a common plane, means for cantilever supporting said recds at corresponding ends thereof, a first contact on the free end of one of said reeds, a sec ond contact on the free end of the other one of said reeds, a third, fixed contact opposite said first contact at one side thereof, a fourth, fixed contact opposite said second con tact at the corresponding side thereof, means for biasing said free ends of said reeds towards said fixed contacts, an electromagnetic coil around said reeds, and permanent magnet means for oppositely polarizing said reeds magnetically.

2. An electromagnetic switch as claimed in claim 1 d in which said first and second contacts are normally in contact with said third and fourth contacts respectively.

3. An electromagnetic switch as claimed in claim 2 in which said biasing means includes reed bases to which said reeds are attached, and includes means for tilting said bases towards said fixed contacts.

4. An electromagnetic switch as claimed in claim 3 in which said permanent magnet means comprises a pair of permanent magnets one on each side of said reeds, one of said magnets having a north pole opposite one of said reeds and a south pole opposite the other one of said reeds, and the other one of said magnets having a south pole opposite said one reed and having a north pole opposite said other reed.

5. An electromagnetic switch as claimed in claim 1 in which said biasing means includes reed bases to which said reeds are attached, and includes means for tilting said bases towards said fixed contacts.

6. An electromagnetic switch as claimed in claim 5 in which said permanent magnet means comprises a pair of permanent magnets one on each side of said reeds, one of said magnets having a north. pole opposite one of said reeds and a south pole opposite the other one of said reeds, and the other one of said magnets having a south pole opposite said one reed and having a north pole opposite said other food.

7. An electromagnetic switch as claimed in claim 1 in which said permanent magnet means comprises a pair of permanent magnets one on each side of said reeds, one of said magnets having a north pole opposite one of said' reeds and having a south pole opposite the other one of said reeds, and the other one of said magnets having a south pole opposite said one reed and having a south pole opposite said other reed.

8. An electromagnetic switch as claimed in claim 7 in which said first and second contacts are normally in contact with said third and fourth contacts respectively.

9. An electromagnetic switch as claimed in claim 8 in which said first and second contacts are electrically connected together.

10. An electromagnetic switch comprising a pair of spaced-apart, aligned, parallel plates of non-magnetic metal, electrical insulation spacing said plates apart at corresponding ends thereof, a bar of metal spacing said plates apart at the other ends thereof, said bar having an opening midway between said plates and having a recess in its outer end connecting with said opening, said bar having corners where said recess connects with said opening, a pair of aligned, wedge-shaped, reed bases within said recess and having sloping inner ends in contact with said corners, a pair of reeds of magnetic spring metal having corresponding ends cantilever supported from said bases on the lines where said sloping ends meet, said reeds extending through said opening, said reeds having corresponding sides spaced apart in a common plane, an electromagnetic coil around said reeds between said plates and between said bar and the free ends of said reeds, a pair of permanent magnets on opposite sides of said reeds between said coil and said free ends, one of said magnets having a north pole opposite one of said reeds and having a south pole opposite the other one of said reeds, and the other one of said magnets having a south pole opposite said one reed and having a north pole opposite said other reed, one of said free ends having a contact surface on one side thereof, the other one of said free ends having a corresponding contact surface on its corresponding side, fixed contacts opposite said surfaces, supporting means for said fixed contacts extending through said insulation, and screws extending through said bases on opposite sides of a plane extending through said lines and threaded into. said bar, said screws being adjustable to tilt said bases and said free ends towards said fixed contacts.

11. An electromagnetic switch as claimed in claim 10 in which said screws are normally adjusted to tilt said bases and said free ends to cause said contact surfaces to. be normally in contact with said fixed contacts.

5 6 12. An electromagnetic switch as claimed in claim It) References Cited by the Examiner in which said tree ends have contact surfaces on their UNITED STATES PATENTS opposite sides, m which there are fixed contacts opposlte said last mentioned surfaces, in which there are supporting 2,636,094 4/53 RPSSeH 200" 93 means for said last mentioned contacts extending through 5 2,758,173 8/56 3 X said insulation, and in which said screws are adjustable to tilt said bases and said free ends towards said last men- BERNARD GILHEANY P r Exammer' tioned fixed contacts. ROBERT K. SCHAEFER, Examiner. 

1. AN ELECTROMAGNETIC SWITCH COMPRISING A PAIR OF REEDS OF MAGNETIC SPRING METAL, SAID REEDS HAVING CORRESPONDING SIDE SPACED APART IN A COMMON PLATE MEANS FOR CANTILEVER SUPPORTING SAID REEDS AT CORRESPONDING ENDS THEREOF, A FIRST CONTACT ON THE FREE END OF ONE OF SAID REEDS, A SECOND CONTACT ON THE FREE END OF THE OTHER ONE OF SAID REEDS, A THIRD, FIXED CONTACT OPPOSITE SAID FIRST CONTACT AT ONE SIDE THEREOF, A FOURTH, FIXED CONTACT OPPOSITE SAID SECOND CONTACT, AT THE CORRESPONDING SIDE THEREOF, MEANS FOR BIASING SAID FREE ENDS OF SAID REEDS TOWARDS SAID FIXED CONTACTS, AN ELECTROMAGNETIC COIL AROUND SAID REEDS, AND PERMANENT MAGNET MEANS FOR OPPOSITELY POLARIZING SAID REEDS MAGNETICALLY. 